The present invention relates to a shuttle assembly usable on a load handling apparatus, such as a stacker crane, and more particularly, to a shuttle assembly having an increased average velocity of movement between the retracted position and the extended position. Although it will be apparent that the present invention is adaptable to many types of load handling apparatus, it is especially advantageous when used with a device such as an automated stacker crane, for which the fastest possible operating cycle is desirable: therefore, the invention will be described in connection with such a stacker crane.
Stacker cranes are commonly used in automated warehouses to put material into the desired bin or storage loction and/or to retrieve material from its storage bin. Typically, a stacker crane moves along the warehouse aisle with the shuttle assembly in the retracted position, and when the crane reaches the designated storage loction, the shuttle assembly either to the left or to the right to deposit or to retrieve the load.
A stacker crane of the type presently known in the art is illustrated in U.S. Pat. No. 3,596,789, assigned to the assignee of the present invention. The illustrated crane utilizes a shuttle assembly which includes a stationary base section, an intermediate section longitudinally movable relative to the base section and a load supporting section longitudinally movable relative to the intermediate section. The term "longitudinal," as used hereinafter in reference to the motion of the various sections of a shuttle assembly, shall mean a direction toward or away from a bin or storage location, i.e., normally perpendicular to the warehouse aisle.
Presently, commercially available shuttle assemblies operate at a substantially constant velocity over most of the travel of the load supporting plate, this constant velocity typically being about 60 ft./min. (18.2 meters per minute). The main drive for the shuttle is provided by a two-speed gear motor, with acceleration and deceleration at the beginning and end of the travel being accomplished by the low speed winding, while the high speed winding provides the constant velocity movement. Attempts at increasing this travel velocity have not been satisfactory, partly because of problems related to the positioning and centering of the shuttle, and partly because of the required acceleration and deceleration of the load supporting plate.